Conventional core of this type, as generally used for manufacturing pneumatic tires, is disclosed, for example, in Japanese Patent Publications JP-11-34062A1, JP-2001-150447A1, and JP-2001-198989A1. The core for manufacturing pneumatic tires disclosed in these patent documents comprises two types of segments, i.e., large segments and small segments, which are alternately arranged in contact with each other and assembled into a toroidal shape, and this assembly is maintained in toroidal shape by means of a pair of retainer rings that are engaged with the assembly from both sides in the axial direction and connected to each other.
With the core for manufacturing pneumatic tires constructed as explained above, after completion of vulcanization with respect to a green tire that has been formed on the outer peripheral surface of the core, the retainer rings are removed so as to release each of the segments from their restrained state. Then, for example, the small segments are initially removed toward the inner peripheral side of the vulcanized tire one by one, with a predetermined sequence, and the large segments are subsequently removed toward the inner peripheral side of the vulcanized tire one by one, with a predetermined sequence, thereby allowing removal of the segments from the vulcanized tire in their disassembled state.
Patent Document 1: Japanese Patent Publication JP-11-34062A1
Patent Document 2: Japanese Patent Publication JP-2001-150447A1
Patent Document 3: Japanese Patent Publication JP-2001-198989A1
With such a conventional technology, each segment has an outer peripheral surface shape that corresponds to the inner contour shape of the product tire in its cross-section, and has the maximum width at the portion of the segment corresponding to the sidewall portion of the tire, which is made larger than the minimum width at the portion of the segment corresponding to the bead portion of the tire. Thus, when each segment is removed toward the inner peripheral side of the tire, it is necessary to forcibly enlarge the relative width between the bead portions of the vulcanized tire, to such an extent as to allow passage of the maximum width portion of the segment. This process is a highly important for avoiding undesirable chipping-off of the tire bead portions by the edge, in the circumferential direction, of the large segment having a planer shape in the form of a sector.
However, when the core is used to form and vulcanize a tire having the maximum inner surface width at the sidewall portions, which is significantly larger than the minimum inner surface width at the bead portions, such as tires having a cross-sectional shape resembling a beret-hat as disclosed in WO 2003/031206A1, there arises a problem that a smooth removal of the segment is practically impossible even if the relative width between the bead portions of the tire is forcibly enlarged to the maximum extent so as to avoid damages or deformation of the bead portions.
The present invention has been accomplished in order to eliminate the problem of the conventional technology as mentioned above. It is an object of the present invention to provide a core for manufacturing pneumatic tires, which allows removal of each segment toward the inner peripheral side of the product tire to be performed positively and in a facilitated manner, even when the tire has the maximum inner surface width at the sidewall portions, which is significantly larger than the minimum inner surface width at the bead portions.